Electrical apparatus



March 28, 1939. P. HAAS ET AL ELECTRICAL APPARATUS Filed Nov. 14, 1935 2Sheets-Sheet INVENTOR Paul Haas BY William T. Taber W Me ATTORNEY Mire28, 1939. P. H AAS ET AL 2,152,539 I ELECTRI CAL APPARATUS Filed Nov.14, 1935 2 Sheets-Sheet 2 INVENTOR W T? 11 BY 1 lElITL a BI ATTORNEYPatented Mar. 28, 1939 UNITED STATES PATENT OFFICE ELECTRICAL APPARATUSDelaware Application November 14, 1935, Serial No. 49,768

Claims.

This invention relates to electrical apparatus and particularly to anaudio frequency amplifier system which is compact, rugged, and easy toassemble.

In audio frequency amplifying systems, particularly at sound pick-upterminals for talking motion pictures or broadcast, it is desirable tohave an amplifying unit located at a point in the proximity of thedetector or microphone. This amplifying unit must, therefore, have assmall over-all dimensions as possible in relation to the amplificationdesired in order that it may be placed near the microphone itself. Theconstruction of the unit must be rugged, so that it may be moved aboutconveniently and particularly during use, without affecting the currentspassing therethrough.

The present invention contemplates such an amplifying unit which hasparticularly small over-all dimensions in relation to its gain ofapproximately 50 db. The over-all dimensions of the unit are about 4 x 5x 8 a handle being provided for carrying the unit from place to place orfor mounting it by suspension. Rubber feet are also provided, so thatthe unit may be used in a standing position.

A particular feature of the invention is the arrangement of the elementsof the unit in such a manner that the terminals are brought adjacent oneanother as closely as possible to permit short interconnectingconductors to be used, while the arrangement of some of the elements ona hinged platform or shelf permits accessibility thereto readily andquickly. The interior of the case is divided into three compartmentsvertically, the lower and upper compartments containing elements such asvacuum tubes, condensers and transformers, while the terminals thereofextend into the center compartment wherein the connections to eachelement are made. The elements mounted in the upper compartment are onthe hinged shelf so that when the casing is removed they may be tippedto one side thus exposing the conductors interconnecting the elements.

Various objects and other features of the invention will be appreciatedand the invention more fully understood from the following descriptionread in conjunction with the accompanying drawings, in which- Fig. 1 isa circuit diagram of the amplifying unit.

Figs. 2 and 3 are side and front views of the amplifier unit showing thepositioning of certain elements therein.

Fig. 4 is a rear view showing the compartments of the unit.

Fig. 5 is a perspective of the unit with a shelf tilted; and

Figs. 6 and '7 are detail views of the tube socket 1 mounting and handlemounting, respectively.

Referring now to a detailed description of the amplifier unit, the samenumerals in each of the drawings relate to identical elements thusshowing the arrangement of the circuit elements of Fig. 1 within theamplifier casing. The amplifier circuit comprises a two-stage amplifieremploying indirectly heated vacuum tubes 5 and 6 together with inputtransformer "l, interstage transformer 8, and output transformer 9.Preceding the input transformer 1 is a low pass filter for thesuppression of radio frequency pick-up and comprises a series inductanceH and shunt condensers l2 and 93. A plate circuit equalizer is alsoemployed in this amplifier which includes resistance elements it and Iiiand condensers i1 and I8. The bias for the tubes 5 and t is obtainedfrom resistances 29 and 2|, respectively, shunted by condensers 22 and23. By-pass condensers 25 are shown in the plate supply for the tubes.Terminal strips are employed for the input, output and tube connectionswithin the unit, the input strip 21 and output strip 28 shown in Fig. 1taking the form of terminal plugs, as shown in Fig. 2. The terminalstrip 29 is shown in Fig. 5 with angle bars for making connections tothe tube elements.

The above description discloses the elements of the electrical circuitin conventional form, while the following description refers to the sameelements as actually employed and positioned. The elements are housed ina casing composed of mounting plates 30 and 3| separated by a gasket 33,plate 31 supporting most of the apparatus, either directly orindirectly. For instance, the condensers i2, I3 and I1 and terminalplugs 21 and 28 are directly attached to the upper portion of the backplate 35 while the transformers 1, 8 and 9 and condensers 25 are mountedin the lower compartment of the unit and attached to a shelf 32 which isattached to plate 3|. Shelf 32 has a right angle extension 45 forming aleg of the unit. A second angle shelf 34 has mounted thereon the tubes 5and 6 and condensers 22 and 23, the tubes being mounted in sockets 35and 36 carrying grid biasing resistance elements and 2!. These tubesockets are mounted in sponge rubber mountings 3'! as shown in detail inFig. 6, to provide a resilient support which prevents microphonicpick-up by the tubes and protects them during any shock occasioned bymoving the unit from place to place. The angle shelf 34 is hinged at 38so that when in normal position the terminals of the condensers 22 and23 and tubes 5 and 6 are adjacent the terminals of the transformers I, 8and 9 and the terminals of the other elements of the amplifier.

A cover member 40 slides over all the units and is bolted to the backplates 30 and 3| by means of long upper bolts 42 and shorter lower bolts43 which are attached to lugs 44 on extension plate 45 and a verticalplate 46. The upper bolts 42 are guided to their threaded sockets 41through a hole in members 48, these members being attached to the upperportion of the cover 40 by means of nuts 49. The handle 50 is hingedupon the members 48, this handle having a hole 5| therein for suspendingthe unit if desired. On the bottom of the casing 40 are rubber footmembers 53, one of which is shown in cross-section in Fig. 3.

In the above-described amplifier unit, a gain of 50 db. has beenobtained Within dimensions approximately 4 x 5" x 8 while the unit isrugged and stable in operation and has been found to be very simple toassemble and to inspect at any time. For inspection it is only necessaryto loosen bolts 42 and 43, remove the cover 40, and tip the shelf 34 tothe position shown in Fig. 5. This exposes all the elements andparticularly the connections thereto to immediate View. The unit hasbeen designed for operation on a microphone boom in the recording oftalking motion pictures, but it is obvious that it is also suitable foruse in any sound pick up system where a very portable amplifying unit isdesired.

What is claimed is:

1. Electrical apparatus comprising a casing, a plurality of horizontalshelves and vertical plates in said casing forming a plurality ofdistinct vertically arranged compartments, and a plurality of electricalelements attached to said shelves disposed in upper and lowercompartments, the terminals of said elements being positioned adjacentone another within a common central compartment and one of said shelvesforming a right angle and tiltable to a vertical position to expose theterminals of said elements.

2. An electrical amplifier comprising a panel, a supporting plate forsaid panel having certain amplifier elements positioned thereon, ahorizontal shelf mounted on said plate and having certain amplifierelements mounted thereunder with the terminals of said elementsextending through the top of said shelf, a second horizontal shelf abovesaid first shelf and spaced therefrom and having certain amplifierelements mounted thereabove with the terminals of said second elementsextending under said second shelf, and means for tilting said secondshelf to a vertical position.

3. An electrical amplifier in accordance with claim 2 in which saidelements are encased within a housing, one side of which is formed bysaid panel.

4. An amplifier unit comprising a panel, a horizontal shelf projectingfrom said panel, a second horizontal shelf having a right angle riserintegral therewith and positioned above said first shelf, said risersupporting said second shelf when said second shelf is moved withrespect to said first shelf, certain electrical elements of said unitbeing attached under said first shelf with terminals thereabove, andcertain other electrical elements being attached above said second shelfwith terminals thereunder, and means to hinge said shelves to oneanother with said riser to provide access to the space between saidshelves for making electrical connections between said elements, saidsecond shelf being tiltable to a vertical position.

5. An amplifier unit comprising a casing, a right angle member withinsaid casing forming a shelf and a lower compartment thereunder, a secondright angle member hinged to said first member and forming a secondshelf and a second compartment above said first compartment, :1. thirdand upper compartment being formed by said second shelf and said casing,a plurality of electrical elements attached to said shelves andpositioned in said lower and upper compartments, and means provided onthe ends of said elements and projecting within said second compartmentfor making interconnections therebetween.

PAUL HAAS. WILLIAM T. TABER.

